In U.S. Pat. No. 4,740,410 various micro-miniature structures are described such as micro gears, pin joints and sliders, all of which may be movable components forming part of or used in combination with a particular micro-mechanical device. In the aforesaid patent, the structures disclosed are formed in a batch process using integrated circuit type semiconductor fabrication techniques that include deposition and etching steps to form movable elements. Once such micro-miniature structural components have been formed, it then becomes necessary to provide a precisely controllable force or motor to move the elements in the desired manner including timing, speed and direction. One approach to the problem of moving micro-miniature elements is to utilize electrostatic force means to form micro motors. One disadvantage with the latter approach is that electrodes for the micromotor rotor and stator poles and also circuit paths and terminals for the required power must be provided. This tends to complicate the construction of micro-miniature devices for some applications.
A general object of the present invention is to provide a system for moving micro-miniature elements utilizing ultrasonic energy instead of electrostatic force.
From work with macroscopic piezoelectric motors it is known (see Inaba et al., Proc. 1987 IEEE Ultrasonics Symp., pp. 745-756) that a traveling flexural ultrasonic wave can move a mechanical element that is coupled through frictional forces to the wave propagation path. In such a macroscopic motor, the flexural wave is generated with bulk piezoelectric transducers shaped and driven so as to produce a flexural motion, an arrangement that is not compatible with micro-miniature structures made using semiconductor fabrication techniques as previously described.
It is therefore another object of the invention to provide an ultrasonic micromotor for driving movable micro- miniature structural elements that are made using semiconductor fabrication techniques so that both the micromotor and the movable elements are highly compatible components of the same basic structural device.
Another object of the invention is to provide a method using ultrasonic wave energy for moving or driving micro-miniature structural elements in predescribed paths, for predetermined distances and at preselected speeds.
Another object of the invention is to provide a method and a device for using ultrasonic energy to move or drive a micro-miniature element along a surface and also to dither it to reduce friction between the elements and the surface.
Still another object is to provide drive means in which electrical potentials are isolated from the region in which motion occurs, for example, as required for certain medical applications of microscopic movable components.
Another object is to provide a mechanical drive or friction reduction of a movable element that produces minimal electrical interference to nearby circuits.
Another object is to provide means for moving quantities of small objects such as solid powdered chemicals and possibly liquid droplets or streams in a controlled fashion.
Yet another object is to provide drive means that will function properly while in a liquid environment even though the liquid might be electrically conducting.